Home owners can choose from an impressive selection of renewable energies. But which is the best for you? Klaus Schmuck of Allianz Climate Solutions discusses their pros and cons. More and more homes are being retrofitted with solarÂ panels. Why is solar power growing so rapidly? Prices have decreased because there are so many suppliers now.

Home owners can choose from an impressive selection of renewable energies. But which is the best for you? Klaus Schmuck of Allianz Climate Solutions discusses their pros and cons.

More and more homes are being retrofitted with solarÂ panels. Why is solar power growing so rapidly?

Prices have decreased because there are so many suppliers now. Chinese solarÂ panel manufacturers have multiplied tenfold and many are already meeting EuropeanÂ standards.

SeveralÂ years ago, potential buyers would have had to ask suppliers how many solarÂ panels were available to buy. The manufacturers could pretty much set theÂ prices. Now we have a surplus of solar panels.

Who should invest in solar panels?

Itâ€™s a good investment for pretty much everyone in Germanyâ€”apart from peopleÂ living in the northwestâ€”because people here produce electricity not for theirÂ own consumption needs but for the grid.

The government guarantees a fixed price for solar power that is much higherÂ than what you pay for electricity from non-regenerative sources. Home owners inÂ Germany arenâ€™t interested in energy independence, but selling at a goodÂ price.

ManyÂ European countries now have similar feed-in tariffs. In southern Europe andÂ northern Africa it also makes sense to use solar for home consumption. And theÂ U.S. is now starting to deploy solar panels on a large scale. California isÂ already a global leader.

WeÂ think that on a global scale grid parity could be achieved by 2015, especiallyÂ in regions with high electricity prices and lots of sun. Solar power shouldÂ then be able to hold its own without subsidies, even against electricity from naturalÂ gas or nuclear power.

Should building owners invest now or will prices forÂ solar panels fall further in two or three years?

In Germany, you should really have invested before the end of 2010. ElectricityÂ from solar panels built before 2011 can be sold at a guaranteed price that willÂ remain stable for 20 years. After that, the guaranteed price will decreaseÂ every year.

ButÂ there is an interesting paradox. Solar panels are usually more expensive inÂ countries with a lot of sun, because profits would be much higher hereÂ otherwise. Even in Germany, solar panels are more expensive in the sunnierÂ south than in the north.

What do you have to consider when installing andÂ running solar panels?

It starts with the building itself; you have to make sure that the roof canÂ really carry the panels. If you are building a new home, you can integrate theÂ panels straight into the roof. If you are retrofitting an old building you haveÂ to mount a frame on the roof, which is actually not that bad, because theÂ panels need good ventilation to work efficiently.

ThenÂ you have to choose the right type of panel for your location. The light is moreÂ diffuse in a big city like Berlin, because of all the smog and haze. In theÂ countryside, you get more direct and intense solar radiation. In general, thereÂ are two types of solar panels. Panels made of so-called thin-film solar cellsÂ are less efficient, but work better with diffuse light. The classicalÂ wafer-based silicon cells can produce more electricity but need direct solarÂ radiation.

OnceÂ your solar panels are up and running they donâ€™t need much maintenance. OnlyÂ bigger installations require an experienced controller. For installations onÂ normal homes, a weekly performance check is enough to verify they are stillÂ running properly.

How long does it take to pay off the initialÂ investment?

That depends on how you have financed the panels. In Germany it usually takes 7Â to 11 years.

WeÂ know how long it takes until a wind turbine has produced the amount of energyÂ needed to build it, usually only a few months. These figures are hard to getÂ for solar panels, because manufacturers use different technologies forÂ production. Researchers from the University of Utrecht found that, depending onÂ the amount of sun you get, it takes two to four years until solar panels haveÂ produced more energy then it took to make them.

AndÂ there is a certain degree of wear and tear on the panels. They have to dealÂ with extreme temperatures, up to 60 degrees Celsius in summer and -20 degreesÂ Celsius in winter. So performance decreases by 0.3 to 0.6 percent every year.Â Most manufacturers therefore guarantee at least 80 percent of performance forÂ the first 20 years.

What kind of alternatives are there to solar power?

There is a lot of work being done on small wind turbines in the UK right now,Â especially in urban areas. But there is one major problem: these small turbinesÂ are installed on roofs or masts that are just too low.

ThatÂ is why conventional wind turbines are mounted on a post thatâ€™s 100 meters tall.Â The wind up there is more stable. In an urban area, you get a lot of turbulenceÂ and the resulting wind speeds just donâ€™t suffice. Furthermore, a turbineÂ creates constant movement that can damage roofs. In the countryside, thingsÂ look different.

InÂ the future, small combined heat and power plants will also be an interestingÂ alternative. The industry will soon be able to deliver these with a competitiveÂ price tag. The question is how to power this unit.

IfÂ you use natural gas, you wonâ€™t do much to improve your carbon footprint. WoodÂ pellets would be better, but then you depend on the wood price. Combining withÂ a biogas plant would be the best solution. There is a pilot village in Germany,Â JÃ¼hnde, where this technology has been used for years.

InÂ many cases, a geothermal heat pump makes sense and can be combined quiteÂ effectively with solar panels. But you have to make sure that the location isÂ suitable. If the difference in temperature between the soil and the surface isÂ too small, the heat pump will become inefficient.

Zero energy houses combine some of these technologiesÂ with first-class insulation. But are they affordable?

They are definitely interesting. In Germany, the KfW bank offers a loan programÂ for such houses. But when you go for a zero-energy house, quality is crucial.Â If the building isnâ€™t done right, heat and moisture will leak into the wallsÂ and you will have mildew.

Governments want toÂ reduce energy consumption tremendously. What does this mean for old buildings?

In the U.S. this trend is already very obvious. There is the Green BuildingÂ initiative that tries to verify that every new building is as energy-efficientÂ as possible. I believe that in ten years time you wonâ€™t be able to find a buyerÂ for a house that has not been built or retrofitted energy efficiently.